Molten metal transfer pipe

ABSTRACT

A transfer pipe for molten metal includes a pipe wall comprised of graphite or ceramic. The graphite ceramic pipe wall can be surrounded by a pipe wall comprising a low thermally conductive material. Both the graphite or ceramic pipe wall and the low thermally conductive pipe wall can be encased in a rigid wall, for example steel. The transfer pipe can communicate with a molten metal pump to provide a system for moving molten metal.

The present invention is directed to a pipe element for transfer of molten metal. The invention is further directed to a system for transfer of molten metal.

BACKGROUND

In the processing of molten metals it is often necessary to transfer the molten metal from one location to another. A molten metal pump is used to transfer molten metal from a furnace, for example, to a ladle, for example. Typically, a transfer pipe is the means through which the molten metal travels.

Several factors, which are listed hereafter in no particular order, are considered and balanced when designing a molten metal transfer pipe line. First, the transfer pipe must be able to withstand the thermal shock of the introduction of molten metal when a pumping element is turned on. Second, the change in temperature through the transfer pipe must be considered. Many situations require that the molten metal drop only a limited number of degrees in temperature between a first location where the metal is stored to a second location to where the metal is delivered. Third, the transfer pipe should be designed so that it can be manufactured at a reasonable cost. Fourth, the transfer pipe should provide an adequate life. Fifth, the molten metal that is pumped through the transfer pipe, for example aluminum, should not stick to the inner wall of the pipe. And sixth, managing the outer skin temperature of the pipe is desirable for safety reasons.

Known attempts to design a transfer pipe with these factors in mind resulted in pipes having a pipe wall made from a low thermal conductivity fiber such as an alumino-silicate fiber available under the trade name FIBERFRAX®. This fiber material is available in a sheet form that can be rolled around a mandrel to form a fiber pipe. The fiber sheets are wetted with a solution. The wet fiber sheet is rolled around the mandrel and then the wetted preform tube is cured in an oven to form the fiber pipe. Alternatively, the fiber can be extruded or vacuum formed and cured to form a fiber pipe.

The fiber pipe is then inserted into a steel pipe. The steel pipe provides mechanical strength to the fiber pipe. The rolled sheet or laminate fiber pipes advantageously provide a tortuous path through which the molten metal must travel if a crack is formed in the pipe wall. This is desirable so the molten aluminum that is passing through the transfer pipe does not contact the steel pipe wall.

Typically, transfer pipes made from the above-mentioned fiber have excellent thermal management properties. Known transfer pipes exhibit about a one degree F. per linear foot heat loss over the length of the pipe. What the known transfer pipes provide in thermal management, however, is traded off in durability.

Attempts to increase the durability of the rolled fiber pipes have included wrapping a first layer of a more durable and more expensive material around the mandrel and then finishing the wrapping with a plurality of layers of the typical fiber sheeting. This method improves durability, however this method of manufacture is difficult and costly. Also, transfer pipes have been produced by casting refractory materials into shape and inserting the cast refractory material into a steel tube. Pipes produced using this method have improved strength; however, thermal losses were great. Coatings have been employed to extend transfer pipe life. Durability of the heat transfer pipe has not been sufficiently improved by these methods to obviate the problem.

SUMMARY

A transfer pipe for molten metal includes a pipe wall comprised of graphite or ceramic. The graphite ceramic pipe wall can be surrounded by a pipe wall comprising a low thermally conductive material. Both the graphite or ceramic pipe wall and the low thermally conductive pipe wall can be encased in a rigid wall, for example steel. The transfer pipe can communicate with a molten metal pump to provide a system for moving molten metal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of a molten metal transfer pipe.

FIG. 2 is a perspective view of a second embodiment of a molten metal transfer pipe.

FIG. 3 is front view of an elbow of a molten metal transfer pipe line.

FIG. 4 is a side view of the elbow of FIG. 3.

FIG. 5 is a cross-sectional view of another embodiment of a molten metal transfer pipe.

FIG. 6 is a perspective view of a molten metal transfer system including the transfer pipe of FIG. 1 or FIG. 2.

DETAILED DESCRIPTION

With reference to FIG. 1, a molten metal transfer pipe 10 includes a first pipe wall 12 and a second pipe wall 14. The molten metal transfer pipe 10 is shown having a circular transverse cross section; however, the transfer pipe can be any number of configurations. The first or outer pipe wall 12 can be made from metal such as steel, similar to the known molten metal transfer pipes, or from another rigid durable material. Since the molten metal transfer pipe 10 is not placed into a molten metal bath, as opposed to a riser tube for a molten metal pump, the transfer pipe 10 need not be encased by a ceramic material. A flange 16 attaches to the ends of the first pipe wall 12 to allow for connection of the transfer pipe 10 to another transfer pipe or connector. The flange 16 includes openings 18 that receive fasteners to connect one pipe to another. Typically, a gasket (not shown) is interposed between two abutting flanges. In an alternative embodiment, the transfer pipe 10 need not include the flange and adjacent transfer pipes can connect to one another using other known connecting methods, which include pipe couplings, clamps, slip fittings and the like.

The second pipe wall 14 can be made from graphite or ceramic. A preferred graphite material from which the second pipe wall 14 can be made is treated graphite available under the trade names ST Graphite, SST Graphite and ZX Graphite available from Metaullics Systems Co. LP. Other similar graphite material, including untreated graphite, can be used that is available from other manufacturers, such as SGL Carbon and Union Carbide. Ceramic material can be materials such as Metaullics Advanced Ceramic (MAC®) available from Metaullics Systems Co., L.P.

With reference to FIG. 2, a third pipe wall 22 can be interposed between the first pipe wall 12 and the second pipe wall 14. The third pipe wall 22 can comprise a low thermally conductive material. One non-limiting example of a low thermally conductive material is the same or similar alumino-silicate material described above. Other low thermally conductive materials can be interposed between the first pipe wall 12 and the second pipe wall 14. Since the third pipe wall does not contact the molten metal, other low thermally conductive materials that may not exhibit the same durability as the above-silicate may also be used.

To manufacture the molten metal transfer pipe 10, the second, i.e. graphite or ceramic, pipe wall 14 can be manufactured in a number of methods. The second pipe wall 14 can be extruded and machined in a known manner. Additionally, the second pipe wall 14 can be made from a graphite cloth that is wrapped around a mandrel, similar to the manufacturing steps involved in making the known sheet fiber pipe. The graphite wrap forms a laminate pipe wall. The graphite pipe wall 14 is manufactured to a desired inner diameter and outer diameter.

For the embodiment depicted in FIG. 1, the second pipe wall 14 is then inserted into the first pipe wall 12. The outer diameter of the second pipe wall 14 and the inner diameter of the first pipe wall 12 are such that little clearance exists between the two pipe walls. Cement, such as QF-150 or QF-180 available from Unifrax Corporation and Metaullics Systems Co. LP can be used to affix the first pipe wall 12 to the second pipe wall 14.

For the embodiment depicted in FIG. 2, the third, i.e. the low thermally conductive, pipe wall 22 can be manufactured in at least two methods. In a first embodiment, a fiber sheet, similar to the fiber sheet described above, can be wrapped around the second wall 14. With the graphite pipe wall 14 being porous, the fiber sheet sticks to the graphite pipe wall. The two pipe walls are then cured in an oven so that the fiber wall 22 cures around the graphite pipe wall 14.

An alternative method of manufacture can include extruding or casting the third pipe wall 22, in a known manner, curing, in a known manner, and inserting the second pipe wall 14 into the third pipe wall. Alternatively, the fiber sheet can be wrapped around a mandrel and cured before inserting the second pipe wall into the third pipe wall. A cement such as QF-150 or QF-180 can be used to secure the second pipe wall to the third pipe wall.

The molten metal transfer pipe 10 can be manufactured according to yet another method, which will be described with reference to FIG. 5. In this embodiment the low thermally conductive material is injected in a gap between the outer pipe wall and the inner pipe wall. In FIG. 5, the inner pipe wall 14 includes terminal flanges 40 that contact the outer rigid pipe wall 12. A gap 42 exists between the central portion (the portion between the flanges 40) of the inner pipe wall 14 and the rigid pipe wall 12. Low thermally conductive material is injected into the gap 42 through an opening 44 in the rigid pipe wall 12. The low thermally conductive material can be injected using any known injector 46. A vent 48 is provided on an opposite end of the pipe 10 and low thermally conductive material can flow through the vent indicating the gap 42 is full.

The embodiment of FIG. 5 is advantageous to provide a transfer pipe 10 having a hardened end for the gasket to contact, i.e. only graphite and steel is exposed, similar to FIG. 1 while employing the benefits of the insulative material between the inner and outer pipe wall. In addition to injecting material into the gap 42 between the inner and outer pipe wall, low thermally conductive sheet material can be wrapped around the inner pipe wall. These methods of manufacture can be advantageous in forming elbows and other fittings.

Fittings can be provided to allow for bends in the molten metal pipe line. With reference to FIGS. 3 and 4, elbows 30 can be made having a graphite pipe wall 32. To manufacture the elbow 30, a first half ring of graphite is formed having a desired diameter. With reference to FIG. 3, the half ring is formed to one side of a central axis 34. A second half ring of graphite is then formed having the same diameter as the first half ring. Portions of material are removed from each ring to form the passageway in the elbow, and the two ring halves are affixed to one another. The ring can then be cut at desired angles, for example three 110 degree elbows can be cut having approximately 30 degrees of waste. The elbow 30 can be covered with a low thermally conductive material (not shown) and a rigid outer pipe wall (not shown) similar to the transfer pipe 10 described above.

A transfer pipe line can be provided using the above described pipe 10 and elbow 30. Other fittings can be provided as well. More thermal loss may be experienced than with known transfer pipes, however, the losses can be limited by using the low thermally conductive pipe wall. Furthermore, for short transfer pipe line runs the loss per foot will be low enough that the low thermally conductive pipe wall may not be needed. What may be sacrificed in thermal management is made up for in durability. The graphite or ceramic inner pipe wall is significantly more durable than known transfer pipe materials.

The transfer pipe 10 can communicate with a riser pipe 40 of a molten metal pump 42 as shown in FIG. 6; however, the transfer pipe 10 can also communicate with other conventional molten metal moving devices such as centrifugal pumps, electromagnetic pumps, gravity feed systems, etc.

The transfer pipe and other components have been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. 

1. A molten metal transfer pipe comprising: an inner pipe wall comprising graphite or ceramic; and a metal outer pipe wall that receives the inner pipe wall.
 2. The pipe of claim 1, wherein the inner pipe wall is cemented to the outer pipe wall.
 3. The pipe of claim 1, wherein the inner pipe wall comprises a graphite laminate.
 4. The pipe of claim 1, further comprising an intermediate pipe wall interposed between the inner pipe wall and the outer pipe wall.
 5. The pipe of claim 4, wherein the intermediate pipe wall comprises a low thermally conductive material.
 6. The pipe of claim 4, wherein the intermediate pipe wall comprises an alumino-silicate material.
 7. The pipe of claim 4, wherein the intermediate pipe comprises fiber sheet.
 8. The pipe of claim 4, wherein the intermediate pipe comprises extruded fiber.
 9. A method for manufacturing a molten metal transfer pipe comprising: forming a graphite or ceramic inner pipe wall; and inserting the inner pipe wall into a rigid non-ceramic pipe wall.
 10. The method of claim 9, further comprising affixing the inner pipe wall to the rigid pipe wall.
 11. The method of claim 9, further comprising wrapping a low thermally conductive material around the inner pipe wall.
 12. The method of claim 11, further comprising curing the low thermally conductive material.
 13. The method of claim 11, wherein the step of inserting the inner pipe wall further comprises inserting the graphite pipe wall and the low thermally conductive material into the rigid pipe wall.
 14. The method of claim 9, further comprising interposing a low thermally conductive material between the inner pipe wall and the rigid pipe wall.
 15. The method of claim 14, wherein the step of interposing a low thermally conductive material comprises injecting low thermally conductive material into a gap between the inner pipe wall and the rigid pipe wall.
 16. A molten metal transfer pipe comprising: an inner graphite or ceramic pipe wall; an intermediate pipe wall comprising a low thermally conductive material; and a rigid outer pipe wall.
 17. The pipe of claim 16, wherein the rigid outer pipe wall comprises steel.
 18. The pipe of claim 16, wherein the low thermally conductive material comprises an alumino-silicate material.
 19. A method for manufacturing a molten metal transfer pipe fitting comprising: forming a first graphite or ceramic portion; removing material from the first graphite or ceramic portion to form a first graphite or ceramic wall; forming a second graphite portion having a complementary shape to the first graphite portion; removing material from the second graphite portion to form a second graphite wall; and attaching the first graphite wall to the second graphite wall.
 20. A molten metal system comprising: a means for moving molten metal; a transfer pipe in communication with the means for moving molten metal, the transfer pipe including an inner pipe wall comprising graphite or ceramic and a metal outer pipe wall that receives the inner pipe wall. 